HOW  TO  MAKE  SALT 


^ATER. 


BY 


Professor  JOHN    LeCONTE 


PUBLISHED    BY   THE 


GOVERNOR  AND  COUNCIL  OF  SOUTH  CAROLINA. 


COLUMBIA,    S.    C: 
CHARLES  P.  PELHAM,  STATE  PRINTER. 

1862 


EJmbersttp  of  Jgorti)  Carolina 


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$Jnlantf)ropic  Societies; 

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Conned. 


RARE  BOOK 
COLLECTION 


THE  UNIVERSITY  OF 

NORTH  CAROLINA 

LIBRARY 


2923 

Conf . 


: 


HOW  TO  MAKE  SALT 


FROM   SEA- WATER. 


BY 


Pkofessor  JOHN"    LeCONTE 


PUBLISHED    BY   THE 


GOVERNOR  AND  COUNCIL  OF  SOUTH  CAROLINA. 


COLUMBIA,   S.    C: 
CHAKLES  P.  PELHAM,  STATE  PEINTEK. 

1862. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  North  Carolina  at  Chapel  Hil 


http://archive.org/details/howtomakesaltfroOOIeco 


MANUFACTURE  OF  SALT  FROM  SEA-WATER. 


FIRST  METHOD. 


BY  THE  SPONTANEOUS  EVAPORATION  OP   SEA-WATER   IN   LARGE    SHALLOW 
BASINS,  CALLED    "  SALT  GARDENS,"  OR  "  SALINES." 

The  process  is  simple,  and  requires  but  little  apparatus  of  any  kind.  The 
first  condition  for  the  establishment  of  a  "saline"  is  a  low,  broad,  level 
ground  on  the  border  of  the  sea,  bay,  or  inlet,  which  can  be  protected  by 
dykes  or  dams  from  the  action  of  the  tides,%  A  shallow  artificial  pond,  or 
reservoir,  is  made  near  the  sea,  and,  if  possible,  below  the  level  of  high 
tides :  so  that  it  may  receive  water  from  the  sea  at  high  tides,  by  means  of 
flood-gates.  When,  however,  tit  is  above  the  sea-level,  the  water  may 
be  elevated  by  means  of  hydraulic  machines.  The  bottom  of  the  pond  or 
reservoir  must  be  laid  out  perfectly  even,  the  soil  must  be  clayey,  to 
retain  the  water,  and  should  be  beaten  hard  and  smooth.  Its  outline  may 
be  irregular,  and  its  depth  should  be  from  three  to  six  feet.  Of  course  its 
size  must  depend  on  the  extent  of  the  ''saline"  which  is  to  be  established. 
In  this  reservoir  the  sea-water  deposits  its  sediments,  becomes  warmed  by 
the  sun's  rays,  and  begins  to  evaporate. 

From  this  reservoir  the  partially  concentrated  brine  is  led  by  a  canal  to  a 
series  of  "rectangular  basins,"  No.  1,  from  ten  to  sixteen  inches  in  depth. 
These  "  basins"  are  divided  into  a  series  of  compartments,  by  means  of  little 
cross  banks,  through  which  the  brine  flows  successively,  in  a  slow  current, 
which  can  be  regulated  at  pleasure.  These  "basins"  should  be  carefully 
prepared  like  the  "reservoir,"  so  as  to  retain  water.  Here,  by  the  action 
of  the  sun  and  wind,  the  water  is  rapidly  evaporated,  and  deposits  a  portion 
of  its  lime,  in  the  form  of  sulphate.  When  the  concentrated  brine  marks 
15°  to  18°  of  Baume's  hydrometer,  it  deposits  a  considerable  quantity  of 
sulphate  of  lime;  and  when  it  marks  25°,  the  whole  of  the  lime  is  deposited. 
From  "basins"  No.  1  the  brine  passes,  in  like  manner,  to  another  series 
of  similar  "rectangular  basins,"  No.  2,  larger  and  more  shallow,  but  more 
carefully  constructed.  In  these  "basins,"  No.  2,  the  remainder  of  the  sul- 
phate of  lime  is  deposited,  and  the  evaporation  is  carried  to  such  a  point 


that  the  water  becomes  a  saturated  brine  by  the  time  it  reaches  the  lower 
side  of  them.  At  this  period  the  volume  of  the  concentrated  brine  is  greatly 
diminished,  and,  marking  25°  of  Baume's  hydrometer,  is  ready  to  be  trans- 
ferred to  the  "salting  tables." 

From  "basins"  No.  2  the  concentrated  brine  passes,  in  like  manner,  to  a 
third  and  last  series  of  similar  "rectangular  basins,"  No.  8,  called  " salting 
tables."  These  are  smaller  and  shallower  "basins,"  carefully  constructed, 
and  divided  into  compartments  communicating  with  each  other,  and  the 
layer  of  water  should  not  be  more  than  three  inches  in  depth.  The  point 
at  which  the  brine  has  reached  a  sufficient  degree  of  concentration  to  be 
introduced  into  the  "salting  tables,"  is  sometimes  judged  of  by  the  water 
becoming  red,  but  the  hydrometer  is.  perhaps,  a  more  reliable  indicator — 
it  should  mark  25°  of  Baunie.  In  the  "salting  tables"  the  brine  soon  be- 
gins to  deposit  salt,  in  the  form  of  crystalline  crusts,  which  are  either  col- 
lected with  rakes  as  soon  as  they  form,  or  allowed  to  accumulate  at  the 
bottom,  until  they  form  masses  of  several  inches  in  thickness.  The  brine 
on  the  "tables"  is  renewed  daily,  or  every  two  days,  according  to  the 
evaporation;  whilst- the  "resewMir,"  as  well  as  "basins"  No.  1  and  No.  2, 
are  constantly  supplied  with  fresh  brine.  The  concentration  of  the  brines 
in  the  "salting  tables"  must  be  carefully  watched,  and  their  density  never 
allowed  to  exceed  28 i°  of  Baume's  hydrometer,  otherwise  a  deposit  of  sul- 
phate of  magnesia  (Epsom  salts)  would  be  formed,  rendering  the  salt  impure. 
The  mother-liquors,  as  they  are  called,  are  run  off  as  soon  as  they  have 
reached  the  above  density :  it  is  usually  necessary  to  draw  them  off  three 
or  four  times  during  the  season.  When  the  salt  has. attained  a  sufficient 
thickness,  it  is  broken  up  and  piled  upon  the  sides  of  the  "tables"  in  large 
pyramids,  which  are  covered  with  clay.  In  these  heaps  the  salt  undergoes 
a  process  of  purification — the  moisture  from  the  clay,  or  from  occasional 
rains,  penetrates  slowly  through  the  mass,  removing  the  more  soluble  foreign 
matters,  and  leaving  the  salt  much  purer  than  before.  If  the  salt  in  these 
heaps  is  too  much  soiled  to  be  sent  into  market,  it  requires  a  process  of 
refining.  For  this  purpose  two  methods  are  employed ;  the  one  consists  in 
simply  washing  the  crude  salt  with  a  concentrated  brine,  which  removes 
the  foreign  salts,  and  a  large  portion  of  the  earthy  impurities.  The  other, 
more  perfect,  but  more  costly  process,  consists  in  dissolving  the  impure  salt 
in  water,  and  adding  a  little  lime  to  precipitate  the  salts  of  magnesia,  always 
present,  after  which  the  filtered  brine  is  slowly  evaporated,  to  obtain  the 
large-grained  salt  used  for  salting  provisions.  When  the  "salines"  yield 
the  coarsely  crystalline  "  bay-salt,"  there  is  no  need  of  these  refining 
processes. 

At  some  of  the  French  "  salines"  the  concentration  of  the  brines  is  carried 
as  far  as  32°  of  Baume's  hydrometer,  and  the  salt  separated  into  three. 

m ' 


qualities.  Between  25°  and  26°  of  Baunie,  the  brine  deposits  25  per  cent, 
of  the  salt  extracted,  which  is  kept  apart,  on  account  of  its  great  purity, 
and  sold  at  a  higher  price  than  the  rest.  In  passing  from  a  density  of  26° 
to  28J°  of  Baunie,  60  per  cent,  more  of  salt  of  second  quality  is  deposited, 
and  from  this  point  to  32°  the  remaining  15  per  cent,  is  obtained,  some- 
what impure  and  deliquescent,  from  the  magnesian  salts  which  it  contains, 
but  preferred  for  the  salting  of  fish,  on  account  of  its  tendency  to  keep 
them  moist. 

The  "salines"  are  usually  cultivated  from  March  to  September,  so  that 
the  process  is  suspended  during  a  large  part  of  the  year.  But  the  French 
have  recently  introduced  improvements,  by  which  the  works  are  carried  on 
throughout,  the  whole  year,  with  an  increase  of  the  produce  by  about  50  per 
cent.  During  the  months  of  autumn  the  evaporation  is  still  carried  on, 
though  more  slowly,  and  brine  is  furnished  marking  from  10°  to  20°  of 
Baume.  This  is  stored  away  in  pits  or  large  wells,  where  the  diluting  effect 
of  the  winter  and  spring  rains  is  but  little  felt,  and  at  the  commencement 
of  the  warm  season  this  brine  is  elevated  into  the  evaporating  "  basins/'  so 
that  the  summer's  labors  are  commenced  with  concentrated  brine,  and  the 
salt  is  all  harvested  in  the  months  of  August  and  September. 

The  foregoing  method,  when  Conducted  on  a  large  scale,  constitutes  the 
most  economical  means  of  making  salt  from  sea-water.  But  the  nature  of 
our  climate  offers  serious  obstacles  to  the  manufacture  of  salt  by  this  pro- 
cess :  jirst,  on  account  of  the  large  quantity  of  rain  which  falls;  and  secondly, 
from  the  great  uncertainty  of  haviug  dry  weather  after  mid-summer,  which 
is  necessary  during,  the  deposition  of  salt  on  the  '-salting  tables."  In  the 
moist  and  rainy  climate  of  Venice  these  difficulties  are  in  a  measure  over- 
come, by  so  arrauging  the  "salting  tables"  that  "in  case  of  heavy  rains  the 
concentrated  brines  are  rapidly  run  off  into  deep  reservoirs  or  large  wells, 
from  which  they  are  again  elevated  when  the  weather  becomes  fine. 

The  marsh  lands,  provided  they  have  an  underlying  stratum  of  clay, 
might  be  prepared  for  extensive  "salines."  In  using  sea-water  of  full 
strength,  the  proportionate  area  of  the  several  evaporating  "basins"  may  be 
as  follows  : 

Area  of  reservoir,  J  of  total  evaporating  surfaces. 

Basins  No.  1,  I  of  total  evaporating  surfaces. 

Basins  No.  2,  J  of  total  evaporating  surfaces. 

Basins  No.  3,  i  of  total  evaporating  surfaces. 
When  the  water  used  is  one-half  the  strength  of  that  in  the  open-ocean,  the 
area  of  basins  No.  3,  the  "salting  tables,"  need  not  be  more  than  one-tenth 
of  the  aggregate  evaporating  surfaces.  Whenever  it  is  practicable,  the  dif- 
ferent basins  should  be  nearly  on  the  same  plane,  so  that  the  brine  may 
flow  from  one  series  to  the  other,  as  its  level  is  reduced  by  evaporation. 


6 

But  when  it  is  necessary  to  construct  the  basins  at  different  levels,  the  brines 
may  be  raised  from  one  series  to  another  by  means  of  wooden  drums,  from 
eight  to  sixteen  feet  in  diameter,  moved  by  steam  or  horse  power. 

The  " saline"  at  Baynas,  in  the  South  of  France,  covers  an  aggregate 
area  of  nearly  371  acres,  and  yields  per  annum  2,125  bushels  (56  pounds 
to  the  bushel)  of  salt  to  each  acre  of  evaporating  surface.  At  other 
French  "salines"  the  average  yearly  produce  is  about  1,594  bushels  to 
each  acre  of  evaporating  surface.  At  the  salt  works  of  the  Lake  of  Berre, 
near  Marseilles,  the  brine  is  scarcely  half  the  strength  of  sea-water,  and  yet 
the  annual  yield  is  966  bushels  of  salt  to  each  acre  of  evaporating  surface. 
The  average  price  of  salt  at  the  last-named  "salines"  is  only  jive  cents  per 
bushel,  but  an  outrageous  impost  upon  it,  amounting  to  ten  times  that  sum, 
enhances  the  price  to  about  fifty-five  cents  per  bushel.  At  these  works  the 
"mother-liquors"  are  used  for  the  production  of  large  quantities  of  sulphate 
of  soda  (from  which  soda  is  manufactured),  as  also  the  salts  of  potash  and 
magnesia. 

SECOND  METHOD. 

BY  "salines"  and  artificial  evaporation  combined. 

In  this  method,  the  evaporating  basins  are  constructed  as  before  indicated, 
excepting  that  basins  No.  3  (salting  tables)  are  omitted.  In  fact,  by  enlarg- 
ing the  area  of  basins  No.  1,  we  might  likewise  dispense  with  basins  No.  2, 
thus  retaining  only  the  reservoir  and  the  series  of  basins  No.  1  as  the 
aggregate  evaporating  surfaces.  The  sea-water  is  first  concentrated  in 
these  basins  by  spontaneous  evaporation,  and  the  brine  thus  obtained  is 
boiled  down,  and  the  salt  extracted.  For  this  purpose  furnaces,  evaporating- 
pans,  and  a  store-house  must  be  provided.  The  pan  is  a  shallow  four-sided 
vessel  of  sheet-iron,  from  nine  to  twelve  inches  deep,  with  flat  bottom,  some- 
what deepened  towards  the  middle,, and  from  ten  to  twenty  feet  or  more  in 
length  and  breadth,  according  to  the  extent  of  the  salt-works.  The  bottom 
of  the  pan  is  supported  by  small  pillars  of  brick-work,  built  from  the  foun- 
dation of  the  furnace,  so  as  to  form,  at  the  same  time,  flues  for  the  distribu- 
tion of  the  heat.  These  flues  are  calculated  to  disseminate  the  flame  as 
uniformly  as  possible  over  the  bottom  of  the  pan,  after  which  it  is  made  to 
pass  out  behind,  to  one  of  the  rooms  of  the  store-house,  called  the  drying- 
chamber,  which  it  heats,  and  then  escapes  by  the  chimney. 

The  process  of  boiling  consists  of  two  distinct  operations :  First,  the  puri- 
fication and  evaporation  of  the  brine  up  to  the  point  of  saturation,  which  is 
called  sludging ;  and  second,  the  crystallization  of  the  salt,  which  is  called 
soccage. 


Sludging. — The  pans  are  rather  more  than  half  filled  with  clear  con- 
centrated brine,  which  is  brought  rapidly  to  a  state  of  violent  boiling,  the 
evaporated  portion  being  replaced  from  time  to  time  by  fresh  brine.  The 
surface  soon  becomes  covered  with  a  dirty  brown  scum,  which,  with  the 
salts  precipitated  at  the  same  time,  collects  as  a  thick  mud.  As  far  as  pos- 
sible, this  must  be  removed  by  means  of  rakes,  but  some  attaches  itself  to 
the  bottom  of  the  pans,  forming  the  pan  scale.  After  twelve  or  fifteen 
boilings,  it  often  increases  to  the  thickness  of  an  inch,  and  must  then  be 
broken  up  by  the  chisel  and  removed.  In  the  meantime  the  solution  of 
salt  becomes  more  concentrated  by  the  constant  evaporation  and  renewal  of 
the  brine,  until  at  last  it  begins  to  crystallize.  This  process  lasts  from  20 
to  24  hours.  When  the  scum  of  crystals  begins  to  form  on  the  surface,  the 
fire  is  lessened,  until  the  temperature  of  the  brine  falls  to  194°  or  167° 
Fahrenheit,  when,  with  slow  evaporation,  the  soccage  begins?  and  lasts  sev. 
eral  days. 

Soccage. — During  this  iime  the  small  floating  crystals  gradually  increase 
in  size  and  sink  to  the  bottom.  When  the  pan  is  kept  at  194°  the  crystals 
have  no  time  for  growing,  and  fine-grained  salt  falls  to  the  bottom ;  at  167° 
they  remain  floating  a  longer  time,  and  produce  salt  of  a  coarser  grain. 
The  temperature  must  not  be  too  much  reduced,  otherwise  the  chloride  of 
magnesium  is  a  source  of  obstruction  to  the  process,  unless  removed  by  the 
addition  of  sulphate  of  soda  or  slaked  lime ;  and,  better  still,  of  both.  To 
remedy  the  crusting  of  the  surface  of  the  brine,  which  sometimes  occurs,  a 
half  an  ounce  of  butter,  or  a  small  quantity  of  powdered  rosin,  may,  if 
necessary,  be  added  to  the  pan.  Sometimes  the  sludging  and  soccage  are 
conducted  in  separate  pans,  the  brine  being  transferred  at  the  proper  time. 

The  purity  of  the  salt  diminishes  towards  the  end  of  the  process  of  soccage; 
for  this  reason  it  must  be  stopped  before  all  the  salt  is  deposited.  It  need 
not,  however,  be  rejected  at  the  end  of  each  boiling;  a  second,  and  some- 
times even  a  third,  charge  may  be  boiled  down  before  the  residue — the 
mother-liquor — is  removed. 

During  the  whole  process  of  soccage  the  salt  is  raked  up  from  the  bottom 
with  long  cullender-shovels,  to  the  edge  of  the  pan,  and  placed  either  in 
wicker-baskets  of  peeled  willow,  or  heaped  upon  boards  which  are  thrown 
back  for  the  purpose,  when,  in  both  cases,  the  brine  runs  back  to  the  pan. 
The  moist  salt,  either  in  the  same  baskets  or  spread  out  upon  hurdles,  is 
then  placed  in  the  drying-chamber,  where  it  is  exposed  to  a  heat  of  120° 
or  130°  Fahrenheit  as  long  as  it  loses  moisture,  when  it  is  packed  up  for 
sale. 

At  Lymington,  in  Hampshire,  England,  the  process  of  obtaining  salt 
from  sea-water  is  similar  to  the  foregoing,  but  somewhat  simpler.  The  sea- 
water  is  concentrated,  by  spontaneous  evaporation,  in  shallow  basins,  to  about 


s 

one-sixth  its  bulk,  before  admitting  it  into  the  boilers.  The  salt  is  not 
fished  out  of  the  pan  and  drained  in  baskets,  but  the  water  is  almost  entirely 
evaporated,  and  the  whole  mass  of  salt  taken  out  at  once,  and  removed  to 
troughs  with  holes  in  the  bottom :  through  these  it  drains  into  pits  under 
ground,  which  receive  the  mother-liquor.  Under  the  troughs,  and  in  a  line 
with  the  holes,  are  fixed  upright  stakes  (old  broom-handles),  and  on  these 
the  salt  concretes  and  forms,  in  the  course  of  ten  or  twelve  days,  on  each 
stake  a  mass  of  sixty  or  eighty  pounds.  These  lumps  are  called  salt-cats. 
They  bear  the  proportion  to  the  salt  made  from  the  same  brine  of  one  to 
one  hundred.  The  mother-liquor  is  reserved  for  the  manufacture  of' Epsom 
salt  during  the  winter  season. 

Cost  of  Boiling. — This  will,  of  course,  depend  on  the  extent  to  which 
the  brine  has  been  concentrated  by  the  process  of  natural  evaporation  in  the 
basins.  If  practicable,  the  brine  should  mark  about  20°  of  Baume  before 
it  is  introduced  into  the  boilers.  To  do  this,  ordinary  sea-water  must  be 
evaporated  to  about  one-eighth  of  its  bulk.  Calculation  shows  that  10,000 
gallons  (of  231  cubic  inches  each)  of  this  concentrated  brine  contains  305 i 
bushels  (of  56  pounds)  of  salt.  Assuming  that  only  eighty-five  per  cent,  of 
it  can  be  conveniently  extracted,  this  quantity  of  brine  should  yield  nearly 
260  bushels  of  salt.  With  tolerably  good  arrangements  for  boiling,  each 
pound  of  wood  should  evaporate  3}  pounds  of  water.  Taking  the  weight  of 
a  cord  of  dry  pine  to  be  equal  to  3,200  pounds  (a  low  estimate),  it  will  re- 
quire about  7J  cords  to  boil  down  the  10,000  gallons  so  as  to  extract  the  260 
bushels  of  salt ;  that  is,  it  will  require  the  burning  of  one  cord  of  wood  to 
every  35}  bushels  of  salt  manufactured. 

Supposing  the  concentration  of  the  sea-water  to  be  carried  only  as  far  as 
at  Lymington,  viz  :  to  one-sixth -of  its  bulk,  or  marking  15°  of  Baum6, 
10,000  gallons  will  contain  about  194}  bushels  of  salt  capable  of  being  ex- 
tracted. In  this  ca*se  about  26}  bushels  of  salt  ought  to  be  made  for  each 
cord  of  wood  burnt. 

THIRD  METHOD. 

BY    SPONTANEOUS    EVAPORATION    IN    GRADUATION-HOUSES    AND    BOILING 

COMBINED. 

The  advantages  of  this  method  are  :  1.  That  all  the  processes  are  con- 
ducted under  shelter,  so  that  the  operations  are  independent  of  rainy  weather. 
2.  That  the  space  required  for  the  works  is.  comparatively  small.  3.  That 
the  arrangements  are  not  costly,  and  may  be  put  up  on  any  desired  scale. 

A  large  reservoir  is  constructed  at  some  point  conveniently  situated  for 
receiving  the  brine  from  the  sea.     Erom  this  the  sea-water  is  pumped  up 


into  a  large  wooden  cistern  on  the  top  of  a  tower  25  or  30  feet  in  height, 
from  whence  it  is  conducted  to  the  graduation-house,  to  be  concentrated. 

Graduation-House. — This  is  a  long,  open  frame  building,  the  longest 
side  of  which  is  exposed  to  the  prevailing  wind  of  the  locality.  The  floor 
of  the  building  is  made  of  a  large  clay  basin,  or  of  strong  wooden  planks, 
intended  to  collect  the  brine  which  has  been  concentrated  by  evaporation. 
The  spaces  between  the  frame  of  the  shed  are  filled  with  bundles  of  twigs 
or  fagots,  so  that  the  building  looks  like  a  vast  wall  of  brush,  20  or  30  feet 
high,  and  from  100  to  1,000  feet  in  length.  The  pyramid  of  fagots  should 
be  ten  feet  thick  at  its  base  and  six  feet  at  its  upper  part.  Under  the  ridge 
of  the  graduation-house,  and  consequently  over  the  middle  of  the  long  wall 
of  fagots,  is  a  long  wooden  trough  or  spout,  perforated  with  holes  at  small 
intervals,  through  which  the  sea-water  flows  from  the  large  cistern  on  the 
tower.  In  this  manner  the  weak  brine  is  made  to  fall  like  a  perpetual 
shower  over  the  vastly  extended  surface  of  the  fagots  into  the  basin  below, 
during  which  it  is  rapidly  concentrated  by  evaporation.  This  partially  con- 
centrated brine  is  again  pumped  up,  and  undergoes  the  same  operation  suc- 
cessively, until  it  is  sufficiently  concentrated  for  boiling.  The  same  brine  is 
usually  passed  four  or  five  times  through  the  fagots  before  it  is  fit  for  boil- 
ing; it  is  then  passed  into,  a  reservoir,  and  kept  for  the  boiling  operations. 
During  these  successive  concentrations  the  fagots  gradually  become  coated 
with  a  crust  of  the  salts  of  lime,  but  one  set  will  last  about  eight  or  ten 
years. 

Of  course  it  is  best  that  this  operation  should  be  conducted  during  the 
warm  season ;  in  fact,  when  the  temperature  is  below  27°  Fahrenheit,  a 
portion  of  salt  is  lost  by  the  reaction  of  the  sulphate  of  magnesia.  But  the 
boiling  may  be  carried  on  at  any  season.  In  general,  the  brine  jit  for  boiling 
should  contain  about  20  per  cent,  of  salt,  that  is,  should  mark  20°  of  Baume\ 
The  boiling  process  is  the  same  as  that  indicated  in  the  second  method,  and 
its  cost  will  be  as  there  estimated.  By  adding  slaked  lime  to  the  reservoir 
of  brine  fit  for  boiling,  the  magnesia  might  be  precipitated,  and  a  purer  salt 
obtained. 

FOURTH  METHOD. 

BY   LIXIVIATING   SALINE   SAND   AND   THEN   BOILING   THE    BRINE. 

This  method  is  employed  in  Lower  Normandy,  and  is  used  for  making 
salt  on  a  small  scale.  A  level  shore  with  a  clean  sand  is  selected,  and  the 
necessary  buildings  are  erected  (covered  sheds,  evaporating-pans,  store- 
houses, &c),  and  an  area  of  three  or  four  acres  is  chosen,  a  little  below  the 
level  of  spring  tides.  The  surface  is  carefully  levelled,  and  rolled  smooth 
and  hard.  It  is  then  filled  with  sand  taken  from  the  shore  at  low  water,  to 
2 


10 

the  depth  of  several  inches,  and  the  sand  is  also  drenched  with  sea-water  at 
high  tide.  It  then  lies  exposed  to  the  sun  and  wind,  which  soon  evaporate 
the  water,  and  the  surface  is  covered  with  a  white  efflorescence  of  salt.  It 
is  then  turned  over  frequently  with  the  shovel,  changing  the  surface  several 
times  a  day,  till  the  whole  is  perfectly  dry.  This  saline  sand  is  carried  to 
the  sheds,  and  the  process  repeated  with  fresh  sand,  till  a  large  quantity  is 
collected.  i 

To  make  the  brine,  the  dry  saline  sand  is  taken  out  of  the  sheds  and 
thrown  into  small  round  pits,  2£  feet  in  diameter  and  12  inches  deep,  the 
bottoms  of  which  are  lined  with  hard  rammed  clay,  mixed  with  straw.  The 
sand  is  then  covered  with  sea-water,  or  with  the  weaker  ley  of  former 
operations,  and,  after  standing  some  hours,  is  drawn  off  into  reservoirs  or 
barrels,' whence  the  evaporating-pans  are  supplied.  The  sand  is  lixiviated 
a  second  time,  and  this  ley  is  reserved  for  a  fresh  portion  of  saline  sand. 
The  boilers  used  on  the  western  coast  of  France  are  about  3 \  feet  square, 
and  4  or  6  inches  in  depth — a  charge  is  worked  off  in  from  2  to  3  hours. 
Three  pans  of  this  size  yield  together  about  50  pounds  of  salt,  but  it  is  of 
rather  inferior  quality  for  preserving  meat. 

FIFTH  METHOD. 

BY     BOILING     SEA-WATER. 

This  method  cannot  be  made  economical  except  where  fuel  is  very  cheap. 
In  Scotland  a  very  good  quality  of  salt  is  made  in  this  manner.  The  boil- 
ing processes  are  identical  with  those  detailed  under  the  second  method, 
excepting  that,  on  account  of  the  weakness  of  the  brine,  the  first  operation 
(sludging)  is  very  much  prolonged. 

Cost  op  Boiling. — Ordinary  sea-water  contains  about  2£  per  cent,  of  its 
weight  of  pure  salt.  Hence,  it  follows  that  10,000  gallons  contain  a  little 
more  than  38  bushels  of  salt,  of  56  pounds  each.  Assuming  that  85  per 
cent,  of  this  can  be  extracted  by  boiling,  10,000  gallons  of  sea-water  will 
yield  nearly  32  \  bushels  of  salt.  To  boil  down  this  quantity  of  sea- water  will 
require  the  combustion  of  7i  cords  of  wood;  that  is,  not  quite  4$  bushels 
of  salt  to  each  cord  of  wood  burnt.  When  the  brine  is  weaker  than  ordi- 
nary sea-water,  of  course  the  yield  will  be  proportionally  smaller,  and  the 
operations  more  expensive.  To  obtain  a  good  quality  of  salt,  all  the  precau- 
tions in  boiling  indicated  under  the  second  method  must  be  observed. 

The  foregoing  abstract  of  the  several  processes  of  manufacturing  salt 
from  sea-water  has  been  prepared  at  the  request  of  a  member  of  the  Exec- 
utive Council  of  the  State  of  South  Carolina. 


